In some Multiple-Input Multiple-Output (MIMO) communication systems, the transmitter adapts its transmission based on communication channel feedback that is produced by the receiver. In some cases, for example in Long-Term Evolution (LTE) and LTE-Advanced (LTE-A) systems, the transmitter selects a precoding scheme for distributing the signal to the various transmit antenna ports based on the channel feedback. An example channel feedback scheme is described in “Correlation Based Explicit Feedback,” document R1-100719 (R1-100423), 3GPP TSG RAN WG1 Meeting, Valencia, Spain, Jan. 18-22, 2010, which is incorporated herein by reference in its entirety.
In some channel feedback methods, the transmitter and receiver use a predefined set of precoding matrices (a “codebook”), and the channel feedback comprises preferred Precoding Matrix Indicators (PMI) that point to precoding matrices selected from the codebook.
Channel feedback schemes that modify the codebook used by the transmitter and the receiver over time based on a signal Spatial Covariance Function (SCF) have been proposed. Such schemes are sometimes referred to as “codebook adaptation” schemes. An example of codebook adaptation is described in “Adaptive Codebook Designs for MU-MIMO,” document R1-091282, Third Generation Partnership Project (3GPP) Technical Specification Group (TSG) Radio Access Network (RAN) Working Group 1 (WG1) meeting, Seoul, Korea, Mar. 23-27, 2009, which is incorporated herein by reference.
The description above is presented as a general overview of related art in this field and should not be construed as an admission that any of the information it contains constitutes prior art against the present patent application.